Valve seat inserts may be installed in the cylinder heads of internal combustion engines to improve durability. Such inserts are often employed in cylinder heads comprised of softer and lighter alloys which may not have the robust strength, hardness, wear and other material characteristics required for high temperature high wear environments. The valve seat inserts are typically press-fitted into a valve seat insert pocket in the cylinder head and are often manufactured from a relatively hard, wear-resistant and heat resistant material such as a cast or sintered metal. When installed in the cylinder head, the valve seat inserts are effective to provide a durable seating surface for the engine's reciprocating valves.
The press-fit mating of the valve seat insert with the cylinder head valve seat insert pocket may result in the formation of minute gaps or crevices at the interface of the valve seat insert and the cylinder head material. During operation of the engine, liquids and vapors, including fuel, water or other contaminants may enter these openings and become trapped between the surface of the valve seat insert and the cylinder head valve seat insert pocket. While the trapped liquids or vapors are relatively benign in engines which operate on fuels containing a relatively low percentage of alcohols, such as most fuels that use ethanol, it may be corrosive in engines operating on fuels containing a relatively high percentage of alcohols, that may include methanol or other corrosive contaminants and components, especially in situations in which the cylinder head is constructed of an aluminum alloy or other light weight, alloyed material.
In engines which utilize fuels containing a relatively high percentage of alcohol (e.g. greater than 15% ethanol/methanol), the trapped fuel, ambient water dissolved in the fuel, vapors or all of them, may form and/or promote the formation of corrosive acids or byproducts which may corrode the cylinder head, the valve seat inserts, or both, in the areas associated with the valve seat inserts. Further, these components may promote dissimilar metal corrosion through the galvanic effect by serving as an electrolyte in contact with the dissimilar metals of the insert and cylinder head. It is also suspected that galvanic corrosion may occur between the dissimilar metal elements on the surface contacting an electrolyte such as, for instance the copper-aluminum (Cu—Al) interface in common aluminum alloys. Over time, such corrosion may affect the durability of the cylinder head and associated valve seat inserts, especially in cylinder heads which are manufactured from an aluminum alloy.
Various methods have been proposed to address corrosion associated with fuels that contain alcohol including coating the cylinder head valve seat insert pocket with epoxy or phenolic sealants prior to installation of the valve seat insert. Such materials however, if misapplied during application to other components of the engine or valves, or combusted during operation of the engine, may present potential contamination issues for devices such as oxygen sensors or other environmental devices and, therefore, must be applied with great care and precision during manufacture of the cylinder head assembly or, should be avoided.
It is therefore desirable to provide a valve seat insert and cylinder head sealing assembly that avoids corrosive activity, especially corrosion which may be caused by, or associated with, fuels containing alcohols such as ethanol and methanol, and that may also include water and other corrosive components.